1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device including a semiconductor element using an oxide semiconductor. An embodiment of the disclosed invention relates to a method for manufacturing a semiconductor device including an oxide semiconductor element with favorable initial characteristics and small characteristic variation in the long term.
2. Description of the Related Art
There are a wide variety of metal oxides and such metal oxides are used for various applications. Indium oxide is a well-known material and is used as a transparent electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. The examples of such metal oxides having semiconductor characteristics are tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like. A thin film transistor in which a channel formation region is formed using such metal oxides having semiconductor characteristics is known (for example, see Patent Documents 1 to 4, Non-Patent Document 1, and the like).
Further, not only single-component oxides but also multi-component oxides are known as metal oxides. For example, InGaO3(ZnO)m (m is natural number) which is a homologous compound is known as a multi-component oxide containing In, Ga and Zn (for example, see Non-Patent Documents 2 to 4 and the like).
Furthermore, it is confirmed that an oxide semiconductor including such an In—Ga—Zn—O-based oxide is applicable to a channel layer of a thin film transistor (for example, see Patent Document 5, Non-Patent Documents 5 and 6, and the like).